Under certain conditions of decompression, gas supersaturation may develop in tissues and blood and cause bubbles to form, with serious medical consequences. The early etiology of decompression sickness has received relatively little attention in the past and is poorly understood. For example, the biophysical basis for the very high in vivo susceptibility to bubble formation has not been established, and essential information is lacking as to where and how the bubbles form. Our long term objective is to increase the understanding of the phenomena that lead to decompression sickness, in order to aid in the development of better procedures for its prevention and treatment. Based on results obtained so far with aqueous solutions, cells and simple organisms, gas micronuclei appear to be far less important in vivo than is commonly assumed; rather, bubbles are generated spontaneously at hydrophobic surfaces. The proposed investigations will focus on (1) how hydrophobic surfaces aid the nucleation of bubbles in aqueous liquids, and (2) the facilitating effect which carbon dioxide may have on this process. The experimental approach involves subjecting aqueous suspensions of particles with the desired surface characteristics to varying levels of nitrogen or carbon dioxide supersaturations by decompressions from elevated saturation pressures, and monitoring the formation of bubbles. By using mixtures of the two gases as well as pure gases, the bubble nucleation properties of each gas can be established. Potential effects of carbonic anhydrase on nucleation by carbon dioxide will be tested. The gas supersaturation threshold for bubble formation will be related to such variables as surface hydrophobicity and physical configurations. Scanning electron microscopy will be used to asses the gross surface characteristics, and hydrostatic pressurizations will be used to evaluate and manipulate the role of gaseous micronuclei generated or trapped in surface pores. Also to be investigated is the possibility that the cytoplasm of some cell types may serve as nucleation sites for bubbles. Mammalian adipose and muscle cells from tissue cultures specifically will be examined. The methods to be used include direct microscopic observations and high speed cinephotomicrographic recordings of events during decompressions, and also assessment of post-decompression damage to the cells. We expect that our experimental approaches will allow us to develop concepts and theories which will be directly applicable to higher animals, including humans.